Understanding of the parameters passed by script
${! #} enter the last parameter
$# number of input parameters
$* enter all parameter strings and treat all parameters as one string.
$n output n parameters
$? The exit status of the previous command, or the return value of the function.
$the current Shell process ID. For Shell scripts, it is the process ID where these scripts are located.
The difference between $* and $@
Both $* and $@ indicate that all arguments passed to a function or script, when not contained in double quotes (""), are marked with "$1"$2". Outputs all parameters in the form "$n".
But when they are enclosed in double quotes (""), "$*" takes all the parameters as a whole and outputs all parameters in the form of "$1 $2 … $n"; "$@" separates the parameters as "$1"$2"... Outputs all parameters in the form "$n".
